Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/color-convert/route.js

@@ -0,0 +1,97 @@
+var conversions = require('./conversions');
+
+/*
+	this function routes a model to all other models.
+
+	all functions that are routed have a property `.conversion` attached
+	to the returned synthetic function. This property is an array
+	of strings, each with the steps in between the 'from' and 'to'
+	color models (inclusive).
+
+	conversions that are not possible simply are not included.
+*/
+
+function buildGraph() {
+	var graph = {};
+	// https://jsperf.com/object-keys-vs-for-in-with-closure/3
+	var models = Object.keys(conversions);
+
+	for (var len = models.length, i = 0; i < len; i++) {
+		graph[models[i]] = {
+			// http://jsperf.com/1-vs-infinity
+			// micro-opt, but this is simple.
+			distance: -1,
+			parent: null
+		};
+	}
+
+	return graph;
+}
+
+// https://en.wikipedia.org/wiki/Breadth-first_search
+function deriveBFS(fromModel) {
+	var graph = buildGraph();
+	var queue = [fromModel]; // unshift -> queue -> pop
+
+	graph[fromModel].distance = 0;
+
+	while (queue.length) {
+		var current = queue.pop();
+		var adjacents = Object.keys(conversions[current]);
+
+		for (var len = adjacents.length, i = 0; i < len; i++) {
+			var adjacent = adjacents[i];
+			var node = graph[adjacent];
+
+			if (node.distance === -1) {
+				node.distance = graph[current].distance + 1;
+				node.parent = current;
+				queue.unshift(adjacent);
+			}
+		}
+	}
+
+	return graph;
+}
+
+function link(from, to) {
+	return function (args) {
+		return to(from(args));
+	};
+}
+
+function wrapConversion(toModel, graph) {
+	var path = [graph[toModel].parent, toModel];
+	var fn = conversions[graph[toModel].parent][toModel];
+
+	var cur = graph[toModel].parent;
+	while (graph[cur].parent) {
+		path.unshift(graph[cur].parent);
+		fn = link(conversions[graph[cur].parent][cur], fn);
+		cur = graph[cur].parent;
+	}
+
+	fn.conversion = path;
+	return fn;
+}
+
+module.exports = function (fromModel) {
+	var graph = deriveBFS(fromModel);
+	var conversion = {};
+
+	var models = Object.keys(graph);
+	for (var len = models.length, i = 0; i < len; i++) {
+		var toModel = models[i];
+		var node = graph[toModel];
+
+		if (node.parent === null) {
+			// no possible conversion, or this node is the source model.
+			continue;
+		}
+
+		conversion[toModel] = wrapConversion(toModel, graph);
+	}
+
+	return conversion;
+};
+